The present invention relates to a demodulator and a radio receiver having such a demodulator and a radio receiver incorporating the same and, more particularly, to a demodulator for digitizing an angle modulated reception signal and, thereafter, for enabling demodulation.
Hitherto, a ceramic discriminator, a quadrature demodulator, or the like has widely been used as a demodulator for detecting a deviation amount of an angle modulated reception input signal from a predetermined center frequency, thereby obtaining a demodulation signal. However, those demodulators need devices such as a ceramic device, inductance device to shift the phase by 90.degree., and the like which are not suitable to realize an IC. On the other hand, a carrier to be processed is limited to a special frequency. Thus, there is a problem of miniaturization such that the application is limited to a heterodyne receiver or the like.
Therefore, in recent years, attention has been paid to a method of miniaturizing a circuit scale (realizing an IC) by using a direct conversion method as a receiving method whereby after two base band signals (hereinafter, referred to as an I signal and a Q signal) which have the same frequency as that of a reception wave as an input signal or an intermediate frequency wave and whose phases are mutually orthogonal and different by only .pi./2 radian were extracted, a channel is selected and a demodulating process is executed and by using a digital demodulator for demodulating the digital signals (I and Q signals) as a demodulator.
An example of the demodulator which is used in the receiver which receives by such a direct detecting method has been disclosed in "DIGITAL RADIO FREQUENCY RECEIVER" of the Official Gazette of International Publication No. WO87/1531.